1. Field of the Invention
The present invention relates to insulated tie plates and, more particularly, to a tie plate insulator for electrically isolating parts of a rail system from each other.
2. Description of Related Art
A rail system is generally divided into sections or blocks for detecting trains which permit more trains to travel on one stretch of track or railroad rails. Each section is electrically isolated from all other sections so that when no train is present, a high electrical resistance can be measured over the parallel railroad rails in that section. When a train enters the section, the train short circuits adjacent railroad rails and the electrical resistance drops, thus indicating that a train is in that section.
A tie plate, typically made of metal, is used to secure a railroad rail against lateral, rotational, and vertical movements. See, for example, U.S. Pat. No. 6,179,215. Railroad rails are generally joined to each other by welding each end or by attaching the ends using a steel rail joint. Generally, high performance, non-metallic rail joints are used for electrically isolating two railroad rails in order to build an electrically isolated section. However, when two separate railroad rail sections are joined using a typical metal tie plate, electrical isolation of the railroad rail sections will not occur because the current will pass from one railroad rail section through the tie plate and then to the adjacent railroad rail section. Non-metallic insulating tie plates are typically very expensive because of the special high-performance materials needed to endure the high tensile and flexural forces acting on the railroad rail. Also, prior art initially utilized unsupported joints, but due to insulated joints and to high rail traffic, the industry has switched to supported joints. However, the supported joints typically have been made of polyurethane, which cannot take the high rail traffic and fail prematurely.
It is, therefore, an object of the present invention to provide an insulated tie plate whereby the above drawbacks are eliminated.